Radar, an acronym for “Radio Detection and Ranging”, systems was originally developed many years ago but did not turn into a useful technology until World War II.
One component of a basic radar system is typically a transmitter subsystem which sends out pulse of high frequency electromagnetic energy for a short duration. The frequencies are typically in the Gigahertz (GHz) range of billions of cycles per second. When such a pulse encounters a vehicle made of conducting material (such as metal), a portion of the energy from the incoming pulse is reflected back. If this reflected energy is of a sufficient magnitude, it may be detected by the receiver subsystem of the radar. The computer subsystem which controls the radar system knows when the pulse was transmitted and when the reflected pulse is received. This computer is capable of calculating the round-trip time, t, between the transmitted and received pulses of this electromagnetic energy. These pulses travel at roughly the speed of light, c, which is approximately 186,000 miles/sec (299,999 km/sec). This distance, D, to the detected target is:D=ct/2Examples of current radars and their associated operating frequency bands and uses are as follows:
LowerUpperNominalBandfrequency (GHz)frequency (GHz)wavelength (cm)Ka34380.8Ku12182X8123C485S2410L1220
Airborne radar functionFrequency bandEarly warningUHF and S-bandAltimeterC-bandWeatherC and X-bandFighterX and Ku-bandAttackX and Ku-bandReconnaissanceX and Ku-bandExtremely small, short rangeKa-band and MMW band
The relationship between radar wavelength, λ, and radar frequency, v is:λ=c/v
The strength, or power, of the reflected signal is described very adequately by the Radar Equation which relates radiated power of the transmitting antenna, the size and gain of the antenna and the distance to the target and the apparent size of the target to the radar at the operating frequency of the radar. This equation is as follows:
            P      _        r    =                    P        t            ⁢              G        2            ⁢              λ        2            ⁢      σ                                (                      4            ⁢            π                    )                3            ⁢              R        4            where:                Pr is the average received power        Pt is the transmitted power        G is the gain for the radar        λ is the radar's wavelength        σ is the target's apparent size        R is the range from the radar to the target        
This apparent size of the target, σ, at a given radar wavelength (or frequency) is referred to as the “Radar Cross Section” or RCS. All other things being equal, it is the RCS that dictates the strength of the reflected electromagnetic pulse from a target at a specified distance from the radar transmitter. From a practical standpoint, the RCS is the sole characteristic of the target which dictates whether the target is detected or not.
The current generation of Stealth technologies relies on five elements used in combination to minimize the size of the RCS of a target:                Radar Absorbent Material (RAM)        Internal Radar-Absorbent Construction (IRAC)        External Low Observable Geometry (ELOG)        Infrared Red (IR) Emissions Control        Specialized Mission Profile        
The RAM approach to Stealth incorporates the use of coatings containing iron ferrite material which basically transforms the electric component of the incoming radar wave into a magnetic field. Consequently, the energy of the incoming radar wave is allowed to dissipate. This is an undesirable outcome of the RAM approach.
The IRAC approach creates special structure known as “re-entrant triangles” within the outer skin covering the airframe of the Stealth aircraft. These structures capture energy from the incoming radar wave within spaces that approximate the size of the wavelength of a particular radar frequency. The problem with this approach is that the triangles can only protect against a particular radar frequency, so that multiple triangles are required or the aircraft can be detected by different frequencies.
The ELOG approach is what gives Stealth aircraft the characteristic angular geometry clearly visible to even a lay observer. This flat, angled shape allows incoming radar waves to reflect or “skip” off the external geometry in all directions. Such a geometric design limits the design possibilities for the aircraft.
IR emissions control techniques deal with the heat (IR) signature of vehicular engine output but this requires a different control technique for each different engine signature.
The combination of the above four techniques is highly effective in reducing the RCS of Stealth aircraft in their own right. Additionally, each Stealth mission is carefully laid out so as to present only the minimized RCS to threat detection radars which have been identified and located prior to the mission. Thus a very specific and well-choreographed flight profile incorporating altitude, airspeed, angle-of attack and other flight parameters is flown by Stealthy aircraft on each and every mission. This causes complication of the mission so that improvements are desirable.
In addition, there are short failings with existing Stealth technologies such as the use of toxic chemicals in the construction, susceptibility to the effects of weather and abrasive materials such as sand, as well as continued high levels of maintenance.
But most importantly, there are two major flaws with current Stealth technology. First of all, the techniques outlined above are a permanent fixture of the airframe and cannot be altered or removed without adversely affecting the either the Stealthy or the aerodynamic characteristics of the Stealth aircraft. As such, non-Stealthy aircraft and other vehicles can not be made to take on Stealthy characteristics once they are constructed, commissioned and deployed.
Secondly, Stealth technologies currently in use cannot alter, adjust, adapt or modulate the RCS of a particular Stealthy design in response to new, different or varying radar frequencies employed by an adversary. As such, current Stealth techniques are static, not dynamic, once deployed.
This invention seeks to remedy these shortcomings.